Prevention of dependency to morphine or delaying to it and
decreasing of tendency to morphine craving and also decreasing in morphine induced hyperalgesia(tolerance) were the aims of this study. Nitric oxide is one of the neurotransmitters, which involves in the Dopamine reuptake in striatum. Dopamine is one of the most important neurotransmitters in reward system in central nervous system and it has a critical role in morphine addiction and dependency, tendency and tolerance to it, so in this study we survied the role of L- NAME as a nitric oxide synthetase (NOS) inhibitor on the prevention of morphine addiction in rats.

In this study we evaluated behavioral changes such as morphine craving by self - administration as a criterion for tendency, dependency by observation of withdrawal syndrom signs (e.g Jumping, wet dog shaking) and also responses to nociceptive condenced bim of light by using tail flick analgesia metric device in sham (consuming tap water), control (consuming increasing doses of morphine sulfate solution from 0.1mg/ml up to 0.4mg/ml) and test (treated with 45 mg/kg of L- NAME 30 minutes before consuming of morphine sulfate solution per day) groups.

The results showed that pretreatment with L- NAME in test group lead to a significant decline in tendency to morphine craving, withdrawal signs and also a significant reversal of morphine induced hyperalgesia.

We concluded that L- NAME is a potent agent in the prevention of morphine addiction.